For an apparatus that performs a heat treatment such as a thin film forming process on a plurality of substrates such as semiconductor wafers (hereinafter, referred to as “wafers”) in a stack there is known a vertical heat treatment apparatus in which a wafer boat (substrate supporter) having wafers mounted in the configuration of a shelf is air-tightly loaded in a vertical reaction tube from below and a heat treatment is performed on the wafers. In the reaction tube, gas nozzles supplying processing gases for generating a heat treatment atmosphere are disposed along the vertical direction of the wafer boat. In addition, heaters constituting a heating mechanism for heating the wafers are provided outside the reaction tube. The heaters are separated and provided in a plurality of, for example, five zones in the vertical direction, which are configured such that the temperatures of the respective zones may be independently adjusted.
In such an apparatus, when the heat treatment on the wafers is terminated, the processed wafers are replaced with unprocessed wafers in the wafer boat from below the reaction tube in a state in which the heaters are continuously energized (the interior of the reaction tube is continuously heated). Then, the wafer boat is raised and a heat treatment is performed on the unprocessed wafers. Here, when the wafer boat is loaded into the reaction tube, the temperature of a lower region in the reaction tube is more easily reduced than the temperature of an upper region therein. Therefore, in order to uniformize the heating temperature between the wafers when the wafer boat is loaded into the reaction tube, the heater in the lowermost zone (or the second lowermost zone and the lowermost zone), from among the above-described five zones, is more strongly energized than the other heaters.
As an example of the above-described film forming process, there is an ALD (Atomic Layer Deposition) method in which a thin film is formed by alternately supplying the processing gases that react with each other and stacking a reaction product of these processing gases. When a high dielectric constant film such as hafnium oxide (Hf—O) is formed as the thin film, the processing gases include, for example, TDMAH (tetrakis dimethyl amino hafnium) gas as a source gas and ozone (O3) gas as a reaction gas. Further, in addition to the hafnium oxide film, the high dielectric constant film includes a zirconium oxide (Zr—O) film, a titanium oxide (Ti—O) film, an aluminum oxide (Al—O) film, and the like. The high dielectric constant film is formed using metal-containing carbide (organic material)-based gas as the source gas. The source gas and the reaction gas are respectively supplied from different gas nozzles. In addition, when the high dielectric constant film is formed, in order to possibly reduce a level of contamination remaining in the high dielectric constant film, the heating temperature of the wafers is set near the thermal decomposition temperature of the source gas.
However, if the already-described zone control is performed when such a high dielectric constant film is formed, there is a concern that the internal temperature of the gas nozzle for supplying the source gas exceeds the thermal decomposition temperature of the source gas. That is, in the case where the heating temperature of the wafers in the reaction tube is set near the thermal decomposition temperature of the source gas, if the temperature of the lowermost zone is set higher than the temperature of the other zones, the internal temperature of the gas nozzle positioned in the lowermost zone easily reaches a temperature exceeding the thermal decomposition temperature of the source gas. Furthermore, if the internal temperature of the gas nozzle exceeds the thermal decomposition temperature of the source gas, accretion occurs easily in the interior of the gas nozzle. Thus, in order to restrain particles or nozzle clogging caused by exfoliation of the accretion, the gas nozzle should be frequently replaced. As a method of restraining the accretion from occurring, there is a method in which a gas such as nitrogen (N2) gas is allowed to flow into the gas nozzle after the source gas is supplied. However, this does not result in much of an improvement.
In the related art, there is known a technique of forming a thin film using a CVD (Chemical Vapor Deposition) method, in which nitrogen gas is discharged from a surface of an injector in order to restrain the reaction between tin tetrachloride and water vapor at the surface of the injector. In addition, there are other techniques known for cooling an injector head or an injector in a single substrate type apparatus. However, the aforementioned techniques have not considered the concern of a temperature distribution of a processing gas in a vertical heat treatment apparatus.